One composition of value in the catalytic cracking of petroleum feedstocks comprises a silica magnesia mixture as matrix, a zeolite as the active catalyst and, optionally, alumina. A general formula by weight for a composition of this type is
______________________________________ silica-magnesia 40% to 90% zeolite 5% to 40% alumina 0% to 40% ______________________________________
These catalyst compositions are required to have certain properties, i.e. good gasoline and LCO selectivity and stability during use for example by resistance to attrition.
The silica-magnesia component must be chemically stable and present the properties of an intimate mixture of the silica and magnesia, that is the silica and magnesia should not be detectable separately, e.g. by IR analysis. The magnesium used in the processing should be retained completely in the product and not be removable by subsequent washing procedures. These requirements are not provided by the processes and products described in the literature or in commercial use.